This proposal will establish a clinical core to recruit and retain HIV- infected subjects for the investigations proposed in the accompanying applications from Drs. Samuel Klein and Kevin Yarasheski. Suitable HIV subjects as well as those currently receiving treatment will be identified and recruited. This will include patients without prior antiretroviral therapy, as well as those receiving potent treatment - with or without protease inhibitors. Significant metabolic syndrome will be defined, for the purposes of these investigations as patients with an abnormal glucose intolerance, hypertriglyceridemia, and central adiposity. Patients with and without this syndrome will be recruited. Of paramount importance, will be subjects who are currently receiving protease-inhibitor based treatments who experience metabolic or other side-effects and who will choose to be switched to alternative regimens. The investigators from the clinical core will ensure that such switches are medically appropriate, maintaining viral suppression where possible using alternative potent antiretroviral regimens. Investigators from the clinical core will monitor patients both during the intensive investigations, and where relevant, during changes in antiretroviral therapy. The proposal projects that approximately twenty new patients can be enrolled in this clinical research each year, with a total enrollment target of 100 subjects. Research will be conducted in the University's General Clinical research center and at the clinics of the AIDS Clinical Trials Unit. We will match enrollment in trials to the demography of the epidemic in St. Louis. We therefore anticipate that at least 35% of enrollment will be from the African- American community and at least 10% will be women.